1. Field of the Invention
The present invention relates to exposure method and apparatus for printing the desired pattern on a photosensitive substrate such as a wafer or a photographic mask and more particularly to an exposure method and apparatus designed to control the amount of light for exposure.
2. Description of the Prior Art
Recently, in the fabrication of semiconductor devices, particularly ICs, there has been a demand for increasingly fine circuit patterns and also a highly accurate exposure control has been required for apparatus which print patterns having linewidths of 1 .mu.m or less on wafers, that is, so-called exposure apparatus.
With exposure apparatus of this type which projects the images of a circuit pattern formed on a glass substrate such as a reticle or photographic mask onto a substrate to be exposed, e.g., a wafer or other photographic mask, generally it is desirable to always project a constant amount of exposure light onto the light-sensitive material (photoresist) applied to the wafer or the photographic mask.